"It's too early in the investigation to determine whether or not he had been radicalized," Ed Reinhold, the FBI special agent in charge, said in a news conference Wednesday in Chattanooga.
The timeline revealed that in three to five minutes at a Naval training center, Abdulazeez, 24, crashed his car into a gate, exited his vehicle armed with an assault rifle and a handgun, fired into a building and then went inside it, "continuing to shoot at those he encountered," said Reinhold. One person inside was fatally wounded.
After walking out a back door, Abdulazeez shot and killed two more in a motor pool area; the final two victims were shot in that same outside location after they returned from helping others in the building to reach secure cover over a fence, he said.
"The heroic actions of the service members doubtlessly saved numerous lives," Reinhold said.
Mary Cabell Kelly
Although police alerted by Abdulazeez's earlier shooting at a recruiting office were in pursuit before the gunman reached the training center, they were not on his bumper and had to pursue him inside the second facility based upon where they heard shots being fired. "As soon as they encountered him," he said, "they engaged him."
It was a police shot that felled the gunman.
"At this time we are treating him as a homegrown violent extremist," said Reinhold, who declined to elaborate on reports that Abdulazeez's uncle had been detained in Jordan. "We believe he acted alone. We don't have any information that anyone else was assisting him on that day."
U.S. Attorney Bill Killian initially called the attack "an act of domestic terrorism," but with no clear link tying Abdulazeez to Islamic extremism, authorities are continuing to try to piece together a motive.
A source close to the investigation tells PEOPLE that Abdulazeez's electronics, including his computer and cell phone records, were being "looked at very closely."
After 9/11, Abdulazeez's father, a soil engineer in the city of Chattanooga's public works department, was investigated by the FBI for sending money overseas, but he was cleared of any wrongdoing.
Born in Kuwait, Abdulazeez had traveled to the Middle East several times, including a seven-month trip to Jordan last year to get clean of drugs and alcohol, a family spokesman said.
"We are looking into what he did there, who he associated with," the source tells PEOPLE. "The family is Palestinian. They lived in Kuwait and Jordan before coming to the United States. We are looking very closely into relatives and associates still living there."
Recovered writings by Abdulazeez and interviews with his family reportedly point to the job he lost in 2013 after a failed drug test, and the fact that he was thousands of dollars in debt, as contributing to his escalating depression prior to the shootings. "We have heard the same reports, and we are investigating," said Reinhold.
But investigators also are looking into his family background. "There was conflict within the family in Chattanooga," the source tells PEOPLE. "The father was strict. The mother at one point wanted a divorce. The father wanted another wife, we are told.
"This kid grew up in this environment. He appeared to hold it together for a while. The question is, when did he change, and why? More important: Did he act alone?
"This is a challenging investigation because very obviously something went awry with this young man," the source says. "The investigation is far from over."
With reporting by Susan Keating
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